In the closing days of World War II, the United States was facing a difficult decision. In the face of increasingly fanatical Japanese resistance during the island-hopping Pacific campaign, American casualties were increased dramatically. 

Fearing that an invasion of Japan would cost hundreds of thousands of U.S. casualties and millions of Japanese, the decision by President Truman to drop the atomic bomb on Japan was not made lightly. The atomic bomb was dropped at Hiroshima and Nagasaki. According to some estimates, more than 226,000 people, mostly civilians, died in the two blasts. Following the bombings, Japan surrendered. It was the only time that nuclear weapons have been used in war. 

By August of 1945, there was little doubt that an invasion of mainland Japan was going to happen. The Japanese had been pushed all the way across the Pacific, had their war industries smashed, and were starving. But they weren’t yet defeated. Although they still controlled parts of New Guinea, the Dutch East Indies, and Indochina, their forces there were cut off and had no hope of coming to the assistance of the Japanese islands. 

The “Little Boy” atomic bomb.

The Japanese still had massive numbers of troops in China but defeats in the Philippines, the Marshall Islands, Iwo Jima, and Okinawa had the U.S. on their doorstep. B-29 bombers could now hit Japanese cities and were close enough to have fighter cover all the way to Japan and back. But those American victories were very costly. Where Japanese casualties had been five to six times that of American troops earlier in the war, by the time Okinawa was finally secured in June 1945, the ratios had dropped to 2-1. Japanese troops would rather fight to the death than surrender. Since the battle of the Philippine Sea, Japanese suicide pilots (kamikaze), had also been taking a toll on American warships and lives.   

In preparation for the planned invasion of Japan (Operation Downfall), the B-29 raids over Japan went from high-altitude precision bombing to low-level area bombing with incendiaries. The aim was to destroy the Japanese war machine by targeting the industries. In many of the largest cities in Japan, most buildings were of paper and wood. The results of the fire-bombing were horrific. Over 100 of Japan’s largest cities and towns were firebombed by June. Just in one bombing of Tokyo, over 100,000 people died. Japanese firefighting equipment was not able to keep up. 

With estimates of U.S. casualties in the planned invasion ever increasing as the Japanese rushed troops back from China and created more homeland divisions, the U.S. decided that the atomic bomb would be attempted. There were even proposals of using poison gas on the Japanese, as well as dropping it with a warning in an unpopulated area but those proposals were rejected. The U.S. created the 509th Composite Group, commanded by Colonel Paul Tibbetts to conduct the drops.

The components for the bomb were delivered by the USS Indianapolis to Tinian on July 26. Fearing that a crash upon takeoff would result in a nuclear explosion, Tibbetts had the engineers modify the Little Boy bomb design to incorporate a removable breech plug that would permit the bomb to be armed in flight.

After the Japanese rejected the Allies’ surrender demand, the mission was given the green light. The primary target was Hiroshima with Kokura and Nagasaki as alternative targets. Tibbetts piloted the B-29 “Enola Gay,” named after his mother. The plane belonged to the 393rd Bombardment Squadron of the 509th Composite Group.